Relationship between the matric suction and the shear strength in unsaturated soil

To understand the shear strength properties for unsaturated soil with different matric suction values, a modified triaxial test device was used. The matric suction is considered an important contributor to unsaturated shear strength properties. In this research, the modified triaxial testing machine is used to control the matric suction and to avoid the turbulence and bubbles during test, which keep the matric suction in positive value. The range of the matric suction used is from (0–100) kPa and the it was applied by increments of (10) kPa in each time. It was concluded that the relationship between the shear strength and the matric suction is divided into two parts, the first part is linear and the second is non-linear. The point between the two parts represents a point of reversal stress the two parts which is also considered as the peak stress point. The matric suction increases the soil elasticity, and all the stress variables also increase the angle of the internal friction between the soil particles. The maximum shear stress occurs at a larger matric suction with increase of confining pressure.